1. Field of the Invention
This invention relates to a method and device for determining imperfections in the interior wall of a pipeline. In particular the extent of corrosion of the interior surface of a fluid-carrying pipeline may be appraised by the method and device of this invention.
2. Summary of the Art
The variation in the profile of a surface may be measured by various methods. For example, in U.S. Pat. No. 3,720,818, a stylus, electrically connected to a transducer consisting of two symmetrical coils, is moved along a surface. As the stylus moves normal to the surface changes of inductance in the transducer coils are measured and utilized as a signal of surface roughness. In U.S. Pat. No. 3,580,062 a feeler point is moved along the surface of a work piece to measure roughness. The feeler point is mechanically connected to an electromechanical transducer for converting the relative movement of the feeler point and the work piece into an electrical signal.
Various methods are also known for detecting and profiling the abnormalities of the internal dimensions of various tubular structures, such as pipelines, heat exchanger tubes, etc. which methods include passing a pig adapted to measure changes in the internal walls of a pipeline through the bore. In U.S. Pat. No. 3,973,441 a pipeline pig is disclosed having a wall-contacting shoe which is electrically coupled to an accelerometer and adapted to measure the change in diameter of the pipe as the shoe accelerates or decelerates radially due to contact of the shoe with various corroded internal surfaces and out-of-round portions of the pipeline. U.S. Pat. No. 4,295,092 describes a probe which forms a capacitor with the internal walls of a pipe for measuring the variance in capacitance occurring whenever the probe passes a corroded section of the interior pipewall. In U.S. Pat. No. 4,301,677 an apparatus utilizing cantilever springs coupled to a strain gauge is used to measure changes in the flexing of the cantilevers as the apparatus contacts undulations in the internal surface of a pipe. Similarly, flexure springs are used in the scanner described in U.S. Pat. No. 4,341,113 to measure tube abnormalities through a strain gauge coupled thereto. This scanner also includes an eddy current sensor to locate the tube abnormality in relation to a contiguous external support plate.
All of the above devices require rather sophisticated and sensitive measuring devices to detect internal surface abnormalities; therefore, these devices are not utilized on a frequent, routine basis. It would be desirable to have a device and method that is relatively inexpensive and durable and therefore can be used for frequent monitoring of internal surface corrosion.
Therefore, it is an object of this invention to provide a relatively inexpensive device for frequent use in measuring the internal condition, vis-a-vis corrosion, of the internal surface of a pipeline or other tubular structure.
It is another object of this invention to utilize an acoustic signal to appraise the condition of the interior surface of a fluid-carrying pipeline.
It is another object of this invention to provide a method for recording changes in the condition of the interior surface of a fluid-carrying pipeline with time.
Other objects and advantages of the invention will be apparent from a careful reading of the specification below.